Homeostasis Flashcards
Describe homeostasis in mammals
Maintenance of a stable internal environment by physiological control systems
Explain the importance of maintaining stable core temperature
if temp too high:
- H bonds in tertiary structure break
- Enzymes denature - active site changes shape - fewer ES complexes
If temp too low:
- Not enough KE so fewer ES complex
Explain the importance of maintaining stable blood pH
Above or below optimal pH, ionic / hydrogen bonds in tertiary structure break
Enzymes denature; active sites change shape and substrates can’t bind
Fewer ES complex
Explain the importance of maintaining stable blood glucose concentration
Too low:
Not enough glucose for respiration so less ATP
Too high:
Wp of blood decreases
Water lost from tissue to blood via osmosis
kidneys can’t absorb all glucose
Describe the role of negative feedback in homeostasis
Receptors detect change from optimum
Effectors respond to counteract change
Returning levels to optimum / normal
Describe positive feedback
Receptors detect change from normal
Effectors respond to amplify change
Producing a greater deviation from normal
Factors that effect blood glucose concentration
Consuming carbohydrates
Respiration
Describe the role of the liver in glycogenesis, glycogenolysis and gluconeogenesis
Glycogenesis - converts glucose to glycogen
glycogenolysis - converts glycogen to glucose
Gluconeogenesis - converts AA to glucose
Explain the action of insulin in decreasing blood glucose concentration
Attaches to receptors of target cells
Causes more glucose channel proteins to join membrane
Increases permeability to glucose so more enters via FD
Also activates enzymes to cindery glucose to glycogen so less glucose creates a concentration gradient so more glucose enters via FD
Explain the action of glucagon in increasing blood glucose concentration
Alpha cells in islets of Langerhans in pancreas detect blood glucose concentration is too low → secrete glucagon:
Attaches to specific receptors on cell surface membranes of target cells
Activates enzymes involved in hydrolysis of glycogen to glucose
This establishes a concentration gradient → glucose enters blood by facilitated diffusion
Explain the role of adrenaline in increasing blood glucose concentration
Attaches to specific receptors on cell surface membranes of target cells
Activates enzymes involved in hydrolysis of glycogen to glucose
This establishes a concentration gradient → glucose enters blood by facilitated diffusion
Describe the second messenger model of adrenaline and glucagon action
Adrenaline / glucagon attach to specific receptors on cell membrane which:
Activates enzyme adenylate cyclase (changes shape)
Which converts many ATP to many cyclic AMP (cAMP)
cAMP acts as the second messenger → activates protein kinase enzymes
Protein kinases activate enzymes to break down glycogen to glucose
Suggest an advantage of the second messenger model
Amplifies signal from hormone
As each hormone can stimulate production of many molecules of second messenger
Which can in turn activate many enzymes for rapid increase in glucose
Compare the causes of types I and II diabetes
Type 1 - There is not enough insulin and usually develops during childhood
Type 2 - Receptors less sensitive to insulin
So there is less uptake of glucose and less conversion to glycogen
Describe how of type I diabetes can be controlled
injecting insulin
Suggest why insulin can’t be taken as a tablet by mouth
Insulin is a protein
Would be hydrolysed by end/exo peptidases
Describe how of type II diabetes can be controlled
Drugs that target insulin receptors to increase sensitivity to increase glucose uptake
Reduce sugar and fat, more exercise, lose weight
Describe the structure of a nephron
Nephron = basic structural and functional unit of the kidney (millions in the kidney)
Associated with blood vessels
Summarise role of different parts of nephron
Bowmans capsule - ultrafiltration
PCT - Selective reabsorption
Loop of henle - maintains sodium gradient in medulla
DCT - Reabsorption of water
Collecting dict - Reabsoprtion of water
Describe the formation of glomerular filtrate
High hydrostatic pressure
Small substances absorbed ie glucose and water which are filtered by capillary basement membrane
Large proteins remain in blood
Describe the reabsorption of glucose by the proximal convoluted tubule
Na+ actively transported out of epithelial cells to capillary
Na+ moves by facilitated diffusion into epithelial cells down a concentration gradient, bringing glucose against its concentration gradient
Glucose moves into capillary by facilitated diffusion down its concentration gradient
Describe the reabsorption of water by the proximal convoluted tubule
Glucose etc. in capillaries lower water potential
Water moves by osmosis down a water potential
gradient
Describe and explain how features of the cells in the PCT allow the rapid reabsorption of glucose into the blood
Microvilli / folded cell-surface membrane → provides a large surface area
Many channel / carrier proteins → for facilitated diffusion / co-transport
Many carrier proteins → for active transport
Many mitochondria → produce ATP for active transport
Many ribosomes → produce carrier / channel proteins
Suggest why glucose is found in the urine of an untreated diabetic person
Blood glucose concentration is too high so not all glucose is reabsorbed at the PCT
As glucose carrier proteins are saturated
Explain the importance of maintaining a gradient of sodium ions in the medulla (concentration increases further down)
So water potential decreases down the medulla
So a water potential gradient is maintained
between the collecting duct and medulla
To maximise reabsorption of water by osmosis from filtrate
Describe the role of the loop of Henle in maintaining a gradient of sodium ions in the medulla in AL
In the ascending limb:
○ Na+ actively transported out (so filtrate concentration decreases)
○ Water remains as ascending limb is impermeable to water
○ This increases concentration of Na+ in the medulla, lowering water potential
Describe the role of the loop of Henle in maintaining a gradient of sodium ions in the medulla in DL
Water moves out by osmosis then reabsorbed by capillaries (so filtrate concentration increases)
○ Na+ ‘recycled’ → diffuses back in
Suggest why animals needing to conserve water have long loops of Henle (thick medulla)
More Na+ moved out → higher Na+ concentration
So water potential gradient is maintained for longer
So more water can be reabsorbed from collecting duct by osmosis
Describe the reabsorption of water by the distal convoluted tubule and collecting ducts
Water moves out of distal convoluted tubule & collecting duct by osmosis down a water potential gradient
Controlled by ADH which increases their permeability
What is osmoregulation?
Control of water potential of the blood (by negative feedback)
Describe the role of the hypothalamus in osmoregulation
Contains osmoreceptors which detect increase OR decrease in blood water potential
Produces more ADH when water potential is low OR less ADH when water potential is high
Describe the role of the posterior pituitary gland in osmoregulation
Secretes (more / less) ADH into blood due to signals from the hypothalamus
Describe the role of antidiuretic
hormone (ADH) in osmoregulation
Attaches to receptors on collecting duct (and distal convoluted tubule)
Stimulating addition of channel proteins (aquaporins) into cell-surface membranes
So increases permeability of cells of collecting duct and DCT to water
So increases water reabsorption from collecting duct / DCT (back into blood) by osmosis
So decreases volume and increases concentration of urine produced
